OpenBSD - Secure Free Operating System  
   OpenBSD aims to produce a free, secure multi-platform operating system that integrates strong cryptography including a current and complete IPSec implementation.
   http://www.OpenBSD.org/

Linux IP Tunnel Mini-HOWTO  
   Instructions on how to setup a IP tunnel under Linux
   http://linas.org/linux/iptunnel.html

Linux FreeS/WAN Project  
   An opensource project and software package for creating IPsec VPNs to and from Linux machines.
   http://www.freeswan.org/

Linux-Sec: VPN Page  
   Collection of Linux VPN HowTos and free software.
   http://www.linux-sec.net/VPN

ENskip  
   A GPL'd port of Sun Microsystems Simple Key management for Internet Protocols
   http://www.tik.ee.ethz.ch/~skip/UsersGuide.html

Secure Forwarding of Services with SSH  
   Contains ssh-ppp perl script to set up a VPN.
   http://csociety.ecn.purdue.edu/~sigos/projects/ssh/forwarding/

PPTP-linux client  
   Linux, FreeBSD and NetBSD client for the proprietary Microsoft Point-to-Point Tunneling Protocol, PPTP.
   http://pptpclient.sourceforge.net/

Tunnel Vision VPN  
   Creates an encrypted Virtual Private Network, or VPN, between two Tunnel Vision-capable sites on the Internet. Authentication is made as secure as possible by sending encrypted passwords first-time, and never thereafter.
   http://open.nit.ca/tunnelv/

OpenVPN  
   SSL/TLS based user-space VPN. Supports Linux, Solaris, OpenBSD, FreeBSD, NetBSD, Mac OS X, and Windows 2000/XP.
   http://openvpn.sourceforge.net

tinc  
   A self-contained VPN solution designed to connect multiple sites together in a secure way. Runs on Linux, FreeBSD, OpenBSD, NetBSD, MacOS/X, Solaris, Windows 2000 and XP.
   http://www.tinc-vpn.org/

Unofficial FreeS/WAN Site  
   Home of Super FreeS/WAN, ZeeS/WAN and FreeS/WAN + X.509 packages, as well as interoperability documentation and patches for additional features and broader compatibility.
   http://www.freeswan.ca

PPTP_GUI Home  
   A graphical user interface to the pptp-client software for Linux & BSD.
   http://pptp-gui.sourceforge.net

Linux VPN HOWTO  
   Setting up a VPN with ssh and ppp.
   http://www.tldp.org/HOWTO/VPN-HOWTO.html

Linux VPN Masquerade HOWTO  
   How to configure masquerading of IPsec and PPTP VPN traffic.
   http://www.tldp.org/HOWTO/VPN-Masquerade-HOWTO.html

OpenVPN GUI  
   A Windows GUI for OpenVPN. Gives a systray icon with a menu to control OpenVPN.
   http://openvpn.se/